The present invention relates to a brake power booster including an actuating rod which is in force-transmitting connection with an actuating pedal, and a device for determining an input force, applied to the actuating pedal, which has a pressure chamber that interacts with a pressure generator and is filled with an elastic substance.
A brake power booster disclosed in German Patent No. 42 08 496 includes a device for determining the actuating force introduced at the brake pedal. The device includes force sensors configured as resistance strain gauges or load cells arranged at the brake pedal which can be realized by pressure-responsive resistors or piezoelectric materials. This means that the pedal force is sensed outside the booster housing. Both sensor types must be calibrated individually. This makes them inappropriate for application in large-series production for cost reasons.
In another brake power booster disclosed in German patent application No. 36 27 279, the actuating force introduced at the brake pedal is determined by way of the pressure which develops in an elastic part upon actuation. For this purpose, there is provision of a piston which bears against the elastic part and is displaceable axially within limits. The piston interacts with a pressure sensor which issues signals proportional to the magnitude of the input force. In order to protect the pressure sensor against damage when very high pedal forces prevail, the pressure sensor is so arranged as to be slidable within limits in an axial direction, counteracting the effect of a compression spring, in opposition to the actuating direction of the brake power booster. A disadvantage in the prior art brake power booster is that, for realization of the principle of determining the input force illustrated, extensive constructive modifications are required in the area of the force transmission between the actuating rod and an output force delivering member. These modifications necessitate considerable effort and structure.
Therefore, an object of the present invention is to disclose arrangements which permit sensing the input force introduced at the actuating pedal without constructive modifications to the force transmission area inside the booster housing. The sensing operation shall be effected at low cost and without necessitating large mounting space.